1. Field of the Invention
This invention relates to an enhanced oil recovery method which comprises injecting a fresh water solution of a pectic substance selected from the group consisting of pectin, pectates and polygalacturonic acid and mixtures thereof into high permeability zones within the reservoir wherein the pectic substances upon contact with brine react to form thick gels thereby effectively reducing the permeability of the high permeability zones.
2. Description of the Prior Art
The crude oil which has accumulated in subterranean reservoirs is recovered or produced through one or more wells drilled into the reservoir. Initial production of the crude oil is accomplished by primary recovery techniques wherein only the natural forces present in the reservoir are utilized to produce the oil. However, upon depletion of these natural forces and the termination of primary recovery, a large portion of the crude oil remains trapped within the reservoir. Also, many reservoirs lack sufficient natural forces to be produced by primary methods from the very beginning. Recognition of these facts has led to the development and use of many enhanced oil recovery techniques. Most of these techniques involve injection of at least one fluid into the reservoir to produce an additional amount of the crude oil therefrom. Some of the more common methods are water flooding, polymer flooding, surfactant flooding, miscible flooding and caustic flooding.
Water flooding, which involves injection of water into the subterranean oil reservoir for the purpose of displacing the crude oil from the porous spaces of the reservoir rock towards the producing wells is the most economical and widely used of the enhanced oil recovery methods. However, water does not displace oil with high efficiency because of the immiscibility of water and oil as well as the high interfacial tension between them. Surfactant flooding involves the addition of one or more surface active agents or surfactants to the water flood for the purpose of minimizing the water flooding problems mentioned above.
Surfactant flooding has become an area of rapidly increasing interest in the last few years, especially in the United States as a large number of mature oil fields have begun to approach their economic limits of production under water flooding programs. Both water flooding and surfactant flooding operations as well as any other fluid flooding method, for that matter, must achieve at least a fair measure of vertical conformance efficiency in order for the flooding operation to be a success. Vertical conformance efficiency is a dimension-less number, usually expressed as a percentage, which is a measure of the reduction in efficiency of a flooding operation due to permeability variations within the reservoir. Indeed, most reservoirs display significant permeability variations throughout their volumes causing fluids to flow preferentially through the high permeability sections leaving portions of the reservoir with lower permeabilities essentially isolated from the effects of the injected fluids. One solution to this problem is to selectively plug the higher permeability streaks in order that the injected fluids be then forced into the previously unswept lower permeability portions of the reservoir. Several solutions have been proposed for this problem, but none has proved to be entirely successful.